Re: S-type rough running

[ToToogood@aol.com]

In a message dated 97-02-14 04:46:37 EST, Sstein Hovard wrote:

<< Lastly a question. I'm considering replacing my brake fluid with 
 silicone when installing my overhauled front calipers (I sent them to 
 Classicar Automotive). I'm interested in pro and cons, and wouldn't 
 mind any practical tips.  Do I totaly drain the system first? Do I 
 rinse it with something before putting in the silicone etc. >>

I installed silicon brake fluid (it was called DOT 5 then) in 1978 or 1979
and have not had any problems with my brake system since.  DOT 5 was very
difficult to get hold of back then, but eventually I found a factory souce.
 I had all the calipers rebuilt with Jaguar kits, replaced the flexible
hoses, and flushed the and slave master cylinders and each of steel brake
lines with close to a gallon of silicon fluid (that hurt because the fluid
was so expensive at the time).  Then I reassembled the entire system, and
added fresh silicon brake fluid.  When bleeding the system, I always used
fresh silicon fluid to top up the reservoirs.

Unlike DOT 3 and DOT 4 mineral based brake fluids, DOT 5 Silicon will not
absorb water.  DOT 3 and DOT 4 brake fluids will absorb the moisture and
distribute that moisture through out the entire system.  Thus, as you flush
the system, most of the moisture is expelled.  But with DOT 5, the moisture
puddles.  Water being heavier than DOT 5, the water puddles at the lowest
spot.  Your brake bleeders, however, at typically at a high spot (to expel
air which has entered the system).  (My comments are based on research I did
in the late 70's and early '80's.  Technology may have overcome these
problems by now.)

Small amounts of water will find their way into the system.  I seem to recall
someone tellling me that the rubber used in brake hose is hydroscopic, that
is, it attracts and absorbs water.  The water eventually finds its way from
the wet atmospheric side to the dry brake fluid side.  Moisture can also
enter the system via the small vent hole in the master and slave reservoirs.
 Notwithstanding the fact that the water has puddled at the lowest point, I
believe it is still important to flush the brake system periodically.  I
would like to say that I do it every 2 or 3 years, but I,m sure there has
been a 5 year streach without flushing.  Nonetheless, all calipers and
cylinders are working properly on my vehicle, and I have had no evidence of
brake system failure whatshowever.

When (if) you do change over, put a big sign on you master reservoir that
your vehicle has DOT 5 (Silicon) brake fluid.  On one occassion, my discrete
DOT 5 label had not been noticed and a helpful service facility topped up the
brake system with DOT 4 after changing my oil.  (In that case, the garage
siphoned out the brake reservoir and flushed the entire system with silicon.
 They recognized their mistake and were very good about correcting it).

Phillip Toogood
1973 E-Type OTS

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